Spectrophotometric determination of nickel(II) in different samples by complexation with some triazolylazo dyes

A new sensitive spectrophotometric method for the determination of nickel(II) with 3-(2-hydroxy-5-acetyl-(L¹),-5-ethoxycarbonyl-(L²),-5-methyl-(L³),-5-formyl-(L⁴),-5-bromophen-1-ylazo)-1,2,4-triazole (L⁵), and 3-(2,4-dihydroxyphen-1-ylazo)-1,2,4-triazole (L⁶) in aqueous media containing 40 vol. % methanol has been developed. The method is based on the formation of stable coloured Ni(II) complexes with stoichiometric ratios 1: 1 and 1: 2 (n(M): n(L)). Linear calibration graphs are obtained up to 7.04 μg cm⁻³ of nickel(II) under optimum conditions attained from investigation of complex formation. The absorption maxima varied from 485 nm to 545 nm and the molar absorptivities ranged from 0.84 × 10⁴ to 4.65 × 10⁴ dm³ mol⁻¹ cm⁻¹ for 1: 1 and 1: 2 (n(M): n(L)) complexes with varying the substituent on the phenolic ring. The optimum ranges for the direct determination of nickel(II) (Ringbom) and the stability constants of the formed complexes are determined. The developed method was applied to the spectrophotometric determination of nickel(II) in some samples with satisfactory results.